1. Field of the Present Invention
The present invention relates to a method for ranging/tracking a target, and more particularly to a method for passively ranging/tracking a target, wherein the direction measurements from two or more laterally displaced passive sensors and associated tracking control devices in a carrier and data from a GPS (Global Positioning System)/IMU (Inertial Measurement Unit) integrated navigation system are processed to provide the three dimensional position and velocity information of a moving target.
2. Description of Related Arts
Nowadays, there is an increasing demand for real-time autonomous vehicles in wide application areas, such as industry, agriculture, health care, military, space, and underwater. Major performance characterization of the real-time autonomous vehicles depends on guidance and navigation processing and the control architecture.
Navigation concerns account for the optimal integration of information derived from multiple navigation sensors, such as GPS (Global Positioning System) receiver, IMU (Inertial Measurement Unit), etc. The guidance laws are optimally matched to generate the desired trajectory shape, based on the position information of the autonomous vehicle from the navigation subsystem and the position information of targets from the target tracking subsystem, so as to satisfy optimality criteria along different phases of the traversed path. Target acquisition and tracking accounts for the increasing desire for autonomy in system design. Vehicles are often required to sense their environment and tracking targets that are crucial to their navigation profile. Target state estimation is required to provide or predict an accurate target state from partial information and noisy sensor data.
Generally, conventional methods for producing range measurements of a target with respect to a carrier are to employ an active sensor, such as radio or acoustic radar or laser rangefinder sensor. The concept of operation of an active ranging/tracking sensor depends on measurement of the traveling time between the active sensor transmitted signals and target reflected signals.
Passive tracking methods offer significant advantages over active tracking methods. Unlike radar, laser, and other active tracking control devices, passive sensors do not emit out any kind of energy. They only receive target emitted energy and transform it to measurement data. This characteristic makes the passive tracking method an ideal technique in reconnaissance and surveillance applications, for it can detect the target but keep itself hidden from any external target, as it emits no signals.
However, in general, a passive tracking sensor can not measure the distance between the target and the sensor, as it is not based on the echoed-signal principle. The passive sensor devices offer only the measurement of the target direction with respect to the carrier in space. Therefore, it is very challenging to estimate the highly accurate three-dimensional position and velocity of a target from standalone passive sensors, under target uncertainties, poorly modeled dynamics, perturbations, nonlinear, and time-varying parameters.
The main objective of the invention is to provide a passive ranging/tracking method, which can provide the three dimensional position and velocity information of a moving target through the information from passive sensors and associated tracking control devices and GPS/IMU integrated navigation system.
Another objective of the invention is to provide a passive ranging/tracking method, wherein the passive pointing direction measurements of a moving target from two or more laterally displaced synchronized passive sensors are used to triangulate to determinate range measurements. The range measurements are further filtered to provide the three dimensional position and velocity information of the moving target.
Another objective of the invention is to provide a passive ranging/tracking method, wherein the pair of passive direction measurements of a moving target derived from two or more laterally displaced synchronized passive image sensors is used to triangulate to determinate range measurements. The range measurements are further filtered to provide the position and velocity information of the moving target.
Another objective of the invention is to provide a passive ranging/tracking method, wherein the position, velocity, and attitude information from an onboard integrated GPS/IMU navigation system are incorporated to provide high accuracy position and attitude information of the carrier to facilitate the passive ranging/tracking computation.
Another objective of the invention is to provide a passive ranging/tracking method, wherein a least squares method is employed in the construction of the algorithm of the passive ranging/tracking to obtain a form of optimal estimation.
Another objective of the invention is to provide a passive ranging/tracking method, wherein an optimization method is employed in the construction of the algorithm of the passive ranging/tracking to obtain a form of optimal estimation.
Another objective of the invention is to provide a passive ranging/tracking method, wherein a nonlinear Kalman filter is employed to achieve an effective, numerically convergent, and highly accurate passive ranging/tracking computation.
In order to accomplish the above objectives, the present invention provides a passive ranging/tracking method performed on a carrier, which comprises the steps of:
(a) producing two or more sets of direction measurements of said target with respect to a carrier, such as sets of elevation and azimuth angle of said target, from two or more synchronized sets of passive sensors through associated tracking control device, wherein said passive sensors are installed on different locations of said carrier;
(b) producing navigation data of said carrier, including position, velocity, and attitude data, using an onboard navigation system;
(c) computing said target range vector measurement of said target with respect to said carrier using said two or more sets of direction measurements; and
(d) extracting said three-dimensional position and velocity information of said target at said current epoch using said target range vector measurement.